The invention relates to a process for manufacturing screws and device for actuating the process. In particular, though not exclusively, the invention relates usefully to a manufacturing process for production of screw-type conveyors.
The prior art teaches manufacturing processes in which a bar, generally straight, flat and having a constant straight transversal section, is wound upon itself so as to form a relatively short spiral which is then lengthened by traction force. The form of the screw thus obtained does not normally correspond to the desired shape, so that it usually has to be re-worked by plastic deformation up until it reaches the desired conformation. The above-mentioned adjustment phase must be performed with considerable precision, and requires long and laborious working times.
GB 242518 discloses a process for manufacturing a worm conveyor comprising the following operations: fixing an end of a longitudinally elongate body to an elongate support; commanding a rotation of tire support about a longitudinal axis of rotation thereof constraining tie elongate body to a guide arranged in proximity of tile support and able to move in a parallel direction to a direction of the axis of rotation of tire support, the body winding spirally about the support by effect of a rotation of tile support and an axial movement of the guide.
EP 677711 discloses a process for manufacturing a freezing drum comprising the winding of a metal strip on a cylindrical surface by deformation of the strip from a rectilinear configuration to a helical configuration driving an edge of the strip into tight contact with the surface. The winding of the metal strip is performed by means of a device equipped with means to make the surface rotate around its own axis while a couple of rollers drive the strip into tight contact with the surface. The rollers are mounted on a movable block which translates along a direction parallel to the axis of rotation of the surface.
A further drawback in the prior art is the fact that manufacturing variable-step screws involves a number of complications. This type of screw is produced, for example, by joining up one after another several lengths of screw having various steps. This is a complicated methodology, nor does it allow for production of screws with progressively-varying steps, but only with discrete changes in step.
The main aim of the present invention is to obviate the above-mentioned limits and drawbacks in the prior art by providing a process which advantageously enables screws to be manufactured simply and economically, especially those screws destined to be used as conveyors.
A further advantage of the invention is to reduce considerably the manufacturing times for the screws.
A still further advantage is the extreme precision and constancy of the results obtained using the process in line with the nominal dimensions of the design specifications, especially concerning the screw step. Furthermore, the invention enables very precise screws to be obtained, whatever the material the screw is made of.
A further advantage of the screw is to enable variable-step screws to be made which are relatively simple and economical.
A further aim of the invention is to manufacture a constructionally simple and economical device for carrying out the above-described process.
These aims and advantages and more besides are all attained by the invention, as it is characterised in the appended claims.
Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of a preferred but non-exclusive embodiment of the invention, illustrated purely by way of a non-limiting example in the accompanying figures of the drawings, in which:
FIG. 1 is a schematic view from above of a device made according to the present invention during its functioning cycle;
FIG. 2 is a lateral view from below of FIG. 1;
FIG. 3 is an enlarged detail of FIG. 1, with some parts removed better to evidence others;
FIG. 4 is the detail of FIG. 3 in a different operative configuration;
FIG. 5 schematically shows the view of FIG. 2, evidencing two different possible operative configurations assumed by the means for guiding the longitudinal body destined to form the screw.